This invention relates to essentially alkali-free PbO-, CaO-, MgO-, ZnO-, BaO-containing silicate-glasses with low B.sub.2 O.sub.3 contents and higher additions of Al.sub.2 O.sub.3 which have very low dielectric loss factors, tan .delta., but at the same time have adequate acid-resistance and small thermal expansion coefficients. Such glasses are particularly well suited for use as insulators in ozone generation by silent corona discharges which are acquiring ever increasing importance for degermination or sterilization purposes, for example as applied to water or air. See, e.g., "Ozoneurs a tubes horizontaux," brochure of Welsbach Corporation, Degremont."
The ozone yield is the greater the smaller the dielectric losses in the glass (heating up of the glass). One measure of this effect is provided by the ratio (tan .delta.)/.epsilon. and, more specifically, ozone yield will be the higher the smaller this value. Considering that the applicable glasses in general have very similar .epsilon.-values, the tan .delta.-values are of critical significance.